Are You Confused About Food Allergy Testing?

Have you or your child ever experienced a full-blown allergic reaction to food? It’s called anaphylaxis, where the skin flushes, the face swells, the heart races, breathing becomes labored and the throat starts to close off. Unless epinephrine is promptly injected, unconsciousness and even death may ensue.

People with food allergies are vigilant about what they eat. So it’s no wonder that parents whose children have food allergies want to know which foods are sensitizers and which are safe.

For about 5% of young children and 3%-4% of adults living in Western countries, food-induced allergic reactions lead to a variety of health problems. These include skin rashes, abdominal cramping and diarrhea, chronic cough, wheezing, and other disorders including anaphylaxis. Most any food can trigger an allergic response, but those responsible for the most significant reactions include milk, egg, peanut, tree nuts shellfish, wheat, and soy. Surprisingly, allergy to additives and preservatives is relatively uncommon.

Most food allergies diminish as we age. About 80% of egg and milk allergies resolve by the age of 16. But only 20% of peanut, tree nut, and shellfish allergies resolve by that age. The prevalence of milk, egg, peanut, and tree nut allergy in infants and children is 2.5, 1.5, 1, and 0.5%, respectively. Whereas in adults, the allergy prevalence drops to 0.3, 0.2, 0.6, and 0.6%, respectively. Peanut allergies seem more persistent over time, and even if successfully suppressed through therapy, can reemerge over time.

Unfortunately, the most common tests for food allergy may not be able to pinpoint which food is causing a person’s adverse reaction, leading to over-diagnosis or misdiagnosis in some instances. Blood tests are used to measure the level of antibodies, called immunoglobulin E (IgE), we make to a particular food. But the presence of IgE doesn’t always mean that a person will have an allergic reaction to the food triggering the IgE response.

Skin testing is thought to be more predictive: A small amount of the food allergen is poked into the skin with a needle. If there’s swelling and redness of a certain amount, the test is positive. But as with elevated IgE levels, it doesn’t mean the person will develop allergic symptoms to the food. This can make it difficult for parents to determine what foods to withhold from their children.

A sampling of blood and skin testing from 2005-2006 found that 12% of U.S. children were sensitive to milk, 9% to peanuts, 7% to egg, and 5% to shrimp. However, many experts believe that as few as one-tenth of those children will have an allergic reaction to those foods. So how can you be sure of your child’s risk to specific foods?

The most reliable test is a food challenge under highly controlled circumstances given to children over the age of three. Administered in a doctor’s office or hospital with life support equipment, foods are typically given orally in capsule form with the identity blinded to the patient, with some placebo capsules included. One by one, over the course of several hours, the capsules are consumed and the child is closely observed for signs of allergic reaction. A negative response may lead to food challenge by a full-sized portion of the food in question.

Of course, not every adverse reaction to food represents an allergic reaction. The food may have been spoiled, or the child might be lactose intolerant or have other digestive disorders. If you suspect your child has a food allergy, consult a specialist to decide on the proper approach to diagnosis, diet modification and even therapy.